1. Technical Field
The present invention relates to a method for managing power limits for a battery.
2. Background
A battery used in an electric vehicle or hybrid electric vehicle (HEV), like any battery, has a finite life. Specifically, the power capability of a battery decreases as the battery ages. HEV batteries are often controlled such that they operate at or near a 50% state of charge (S.O.C.), with a full battery power being available over some range of states of charge. For example, a battery in an HEV may be controlled such that the S.O.C. is in the range of 40%-60%. When a battery operates outside its desired S.O.C. range, the power limit will be reduced so that the battery is not asked to exceed its capability on either the charge or discharge side.
As a battery ages, its power capability decreases, and the power limits must be accordingly reduced both inside and outside the desired S.O.C. operating range. Because the power limits can be represented by a curve, one way to reduce the power limits is to reduce the entire curve by some power value to ensure that the entire curve remains under the power capability curve at every S.O.C. This method may have the disadvantage of significantly reducing the power limits over the entire S.O.C. operating range, when in fact, it may be possible to have a higher power limit over at least some of the S.O.C. operating range.
Therefore, it would be desirable to have a control strategy for managing battery power limits such that higher power limits are made available even after a battery ages and its power capability is reduced.